Protein absorption at the intestinal level is commonly believed to consist of absorption of intact dipeptides but there are peptide hydrolases present on the intestinal brush border that have specific activities and substrate specificities making them ideally suited to mediate digestion on the intestinal surface membrane. However, their role in digestion has not been established. We propose to define their role in protein digestion-absorption. By use of automated peptide-amino acid analysis, the capacity of the major intestinal surface amino-oligopeptidase in rat and man to hydrolyze several test oligopeptides will be precisely determined. The initial oligopeptide is hydrolyzed by removal of an N-terminal amino acid and subsequent hydrolysis of the smaller peptide products then occurs. The reactions may be sequential or, if the smaller peptides have high affinity for the enzyme, essentially simultaneous. After the kinetics of the enzyme have been established, correlation will be made with the fate of oligopeptides when exposed to the intact intestinal surface in vitro (sacs, rings) and in vivo. This should help define the functional role of the intestinal surface enzymes in protein digestion. In order to determine whether surface hydrolysis or intact absorption is predominant, intestinal perfusion studies with tetrapeptides will be compared to perfusion of the constituent smaller peptides and amino acids in normal man and patients with intestinal malabsorption or pancreatic insufficiency. The regulation of the intestinal amino-oligopeptidase will be studied in vivo in rats by determination of degradation of the enzyme after H3-amino acid pulse-labelling. The half-life for enzyme in normal animals will be compared with that for those on a low protein or amino acid diet to determine whether substrate stabilization is the important regulator. These studies should elucidate the role of intestinal surface peptide hydrolases in protein absorption in health, in disease states and in malnutrition. BIBLIOGRAPHIC REFERENCES: Smithson, K.W. and Gray, G. M. Intestinal surface hydrolysis of peptides. Clinical Research 23:257, 1975. (Abstract). Wojnarowska, F. and Gray, G. M. Intestinal surface peptide hydrolases. I. Identification and characterization of three enzymes from rat brush border. Biochem. Biophys. Acta 403:147-160, 1975.